#include<bits/stdc++.h>
using namespace std;
int main()
{
	long long d,i,sum=0,day=0,t=1,coin=0;
	cin>>d;
	while(t<=d)
	{
		day++;
		coin++;
		for(i=1;i<=day;i++)
		{
			sum+=coin;
			t++;
			if(t>d)
			break;
		}
	}
	cout<<sum;
    return 0;
}
